Trigger circuitry for fast, low-power state transitions

ABSTRACT

An n-type transistor and a p-type transistor are connected in series such that, when the two transistors are turned on, current flows from the collector of the n-type transistor to the collector of the p-type transistor. A positive-feedback capacitor is connected between the collector of one transistor and the base of the other transistor. The two transistors turn on together when the base voltage of the n-type transistor exceeds the base voltage of the p-type transistor by at least the sum of the turn-on threshold voltages of the two transistors and (i) the two transistors turn off together when the base voltage of the n-type transistor fails to exceed the base voltage of the p-type transistor by at least that sum. The positive-feedback capacitor ensures that the two transistors turn fully on and off together. In certain embodiments, the circuitry can be controlled to operate as a current pulse generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/281,384, filed on Feb. 21, 2019, which claims the benefit of thefiling date of U.S. provisional application No. 62/635,584, filed onFeb. 27, 2018, and U.S. provisional application No. 62/754,628, filed onNov. 2, 2018, the teachings of both of which are incorporated herein byreference in their entirety.

BACKGROUND Field of the Invention

The present invention relates to electronics and, more particularly butnot exclusively, to circuits having state transitions, such as currentpulse generators used in power converters that perform demand pulseregulation such as described in U.S. Pat. No. 9,071,152 (“the '152patent”), the teachings of which are incorporated herein by reference intheir entirety.

Description of the Related Art

This section introduces aspects that may help facilitate a betterunderstanding of the invention. Accordingly, the statements of thissection are to be read in this light and are not to be understood asadmissions about what is prior art or what is not prior art.

In a power converter or other galvanically isolated circuit, it issometimes necessary to send digital information across a galvanicbarrier. A dedicated signal transformer may be used as that barrier, ordigital signals may be transmitted through a power transformer or othergalvanic barrier. In a power converter, it is sometimes desirable for aslowly changing feedback signal to cause a digital event at a particularthreshold voltage. Logic gates or comparators may be used to generatesuch a digital event, but a conventional logic gate or comparator inputwill draw additional current when the feedback signal lingers near thethreshold voltage. That additional current drawn will necessarily reduceefficiency.

SUMMARY

Current pulse generators are described herein that, in response to aslowly changing voltage or current input level, generate a fast edge fordigital signaling, for example, through galvanic isolation circuitry.The circuits described can consume relatively little power and cancombine the functions of a low-power comparator, a fast-edged pulsegenerator, and a maximum rate limiter.

A current pulse generator, also referred to herein simply as a pulsegenerator, is a circuit that generates one or more current pulses. Apositive current pulse is characterized by a rapid rise in current(i.e., a fast leading or rising edge) followed soon after by a rapiddrop in current (i.e., a fast trailing or falling edge), and vice versafor a negative current pulse. The time between successive current pulsesis typically much longer than the duration of each current pulse.

In at least one embodiment, a current pulse generator produces currentpulses having extremely fast rising and falling edges in response to acontrol signal having relatively slow transitions, while consumingrelatively little power. Other possible advantages include tolerance ofa wide operating voltage range, an extremely wide range of operativeoutput pulse frequencies, and a presettable maximum output pulsefrequency.

In at least one embodiment, complimentary pairs of pulse generators forma digital hysteretic buffer producing fast rising and falling edges inresponse to slowly changing input voltage while consuming relativelylittle power.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will become more fully apparent from thefollowing detailed description, the appended claims, and theaccompanying drawings in which like reference numerals identify similaror identical elements.

FIG. 1 is a schematic block diagram of an isolated power converter thatemploys demand pulse regulation (DPR) as described in the '152 patent;

FIG. 2 is a schematic circuit diagram of the demand pulse generator, thesignal transformer, and the pulse detector of FIG. 1 showing details forone possible implementation of the demand pulse generator;

FIG. 3 shows simulated SPICE waveforms for the power converter of FIGS.1 and 2;

FIG. 4 is a schematic circuit diagram of the demand pulse generator, thesignal transformer, and the pulse detector of FIG. 1 showing details foranother possible implementation of the demand pulse generator using FETswitches;

FIG. 5A is a schematic circuit diagram of the demand pulse generator,the signal transformer, and the pulse detector of FIG. 1 showing detailsfor adding single-bit auxiliary digital signaling;

FIG. 5B shows simulated waveforms for the single-bit auxiliary digitalsignaling circuitry of FIG. 5A in operation;

FIG. 6A is a generalized schematic circuit diagram of a pulse generatoraccording to certain embodiments of the invention;

FIG. 6B shows simulated SPICE waveforms for the circuit of FIG. 6Aoperating as a gated, voltage-controlled oscillator;

FIG. 6C shows simulated SPICE waveforms for the circuit of FIG. 6Aoperating as a variable delay generator;

FIG. 7 is a generalized schematic circuit diagram of a pulse generatoraccording to certain other embodiments of the invention;

FIG. 8 is a generalized schematic circuit diagram of a pulse generatoraccording to certain other embodiments of the invention;

FIG. 9 is a schematic circuit diagram of a hysteretic buffer formed froma complementary pair of pulse generators, according to certainembodiments of the invention;

FIG. 10 is a schematic circuit diagram of a hysteretic buffer withoptional input and output buffering;

FIG. 11 shows simulated SPICE waveforms simulated for a medium speedversion of the hysteretic buffer of FIG. 9 for upper and lower voltagerails at 5V and 0V, respectively; and

FIG. 12 is a schematic circuit diagram of a hysteretic buffer withalternative input structure.

DETAILED DESCRIPTION

Detailed illustrative embodiments of the present invention are disclosedherein. However, specific structural and functional details disclosedherein are merely representative for purposes of describing exampleembodiments of the present invention. The present invention may beembodied in many alternate forms and should not be construed as limitedto only the embodiments set forth herein. Further, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting of example embodiments of the invention.

As used herein, the singular forms “a,” “an,” and “the,” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It further will be understood that the terms “comprises,”“comprising,” “includes,” and/or “including,” specify the presence ofstated features, steps, or components, but do not preclude the presenceor addition of one or more other features, steps, or components. It alsoshould be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

In certain embodiments, a current pulse generator of the presentinvention functions as a demand pulse generator on the secondary side ofan isolated power converter having secondary-side control, such as thepower converter 100 of FIG. 1, which is described in further detailbelow. Current pulse generators of the present invention can be used inpower converters for a variety of applications, for example, to convertan AC or DC input signal into a DC output signal to drive an outputload. Any slowly changing signal connected to a logic input can causeextra power to be consumed when the slowly changing signal is in betweena valid high and a valid low logic level. That extra power will reducepower converter efficiency, particularly at low loads. In one example,the input to the demand pulse generator is the slowly changing output ofan error detector, which is representative of the difference between theconverter's output voltage or current and a desired reference voltage orcurrent. That error signal may be proportional when produced by anamplifier or digital when produced by a comparator.

In response to the error signal, the demand pulse generator triggers,producing one or more demand pulses that are transmitted from theconverter's secondary side to the converter's primary side via theconverter's galvanic isolation circuitry, where each demand pulse turnson the converter's primary-side switch to transfer an amount of powerfrom the primary side to the secondary side via the converter's powertransformer. Those demand pulses should have a fast leading edge, thatis, a fast rise or fall time depending on whether the demand pulse is apositive or negative current pulse, in order to better propagate throughthe galvanic isolation circuitry. In a low-power circuit, the rate ofchange of the error signal is expected to be much slower than the edgerate desired for the demand pulses. A desirable demand pulse generatorwill operate over a wide voltage range and can set a maximum frequencyfor the generation of demand pulses. A programmable unijunctiontransistor (PUT) or silicon controlled switch (SCS) could be used as themain active element in the demand pulse generator. As described furtherbelow, the demand pulse generator shown in FIG. 2 uses a discrete n-typetransistor paired with a discrete p-type transistor to perform a similarfunction while consuming less power.

The demand pulse generator taught in FIG. 4 of the '152 patent employsan oscillator that always runs at the maximum demand pulse frequencyeven when the demand pulses are generated at a lower rate (byselectively blocking certain oscillator pulses). The demand pulsegenerators described herein run at the desired demand frequency, therebysaving power at lower demand pulse rates. Furthermore, the demand pulsegenerators described herein begin to operate at under 3 volts of supplyvoltage, which simplifies start-up.

FIG. 1 is a schematic block diagram of an isolated power converter 100that employs demand pulse regulation (DPR) as described in the '152patent. The power converter 100 has a primary side 110, which receivesDC (e.g., rectified AC) input power at the input node 112, and asecondary side 130, which generates output power at the output node 136.The primary and secondary sides are galvanically isolated by twogalvanic barriers: a power transformer T1 and a signal transformer T2.The secondary side 130 is designed to generate demand pulses DP that areconveyed to the primary side 110 via the signal transformer T2 toinstruct the primary side to transfer power to the secondary side viathe power transformer T1 as needed to satisfy the demand at the outputnode 136.

The primary side 110 of the power converter comprises a switch driver122 powered from the input node IE, a main switch 116 (e.g., a FET orbipolar transistor), a pulse detector 120, and two transformer windings:the primary winding 114 of the power transformer T1 and the secondarywinding 118 of the signal transformer T2. Note that the secondarywinding 118 of the signal transformer T2 is on the primary side 110 ofthe converter, while the primary winding 134 of the signal transformerT2 is on the secondary side 130 of the converter. The primary side 110is designed such that the switch driver 122 turns on the main switch 116whenever the pulse detector 120 detects a demand pulse DP on thesecondary winding 118 of the signal transformer T2, as indicated by thesignal PDO. Turning on the main switch 116 enables the input currentfrom the input node 112 to flow through the primary winding 114 of thepower transformer T1, thereby energizing the primary winding 114 of thepower transformer T1. The switch driver 122 determines when to turn offthe main switch 116, based on voltage, current, or time, or acombination thereof, similar to the functionality described in the '152patent. When the main switch 116 turns off, power is transferred to thesecondary side 130 of the converter via the power transformer T1.

The secondary side 130 of the power converter comprises the secondarywinding 132 of the power transformer T1, the primary winding 134 of thesignal transformer T2, the output node 136, filtered by filter capacitor138, a reference generator 140 generating reference voltage REF, anerror amplifier 142 producing a feedback signal FB, a demand pulsegenerator 144, a rectifier (i.e., diode D1), a capacitor 146 functioningas a local power supply, optional synchronous rectification circuitry148, and optional switch S1. If the synchronous rectification circuitry148 is present, then the diode rectifier D1 may be intrinsic to theswitch S1.

The error amplifier 142 generates an analog feedback signal FBresponsive to the difference between the reference voltage REF and theoutput voltage 136 and applies that feedback signal FB to the demandpulse generator 144. When the output voltage 136 is relatively low, thefeedback signal FB will be low and the demand pulse generator 144 willoperate at or near its maximum frequency. When the output voltage 136 isrelatively high, the feedback signal FB will be high and the demandpulse generator 144 will not operate. When the output voltage 136 is atan intermediate voltage, the demand pulse generator 144 can generatedemand pulses at an intermediate rate.

In the embodiment of FIG. 1, the demand pulse generator 144 receives itsoperating power from the capacitor 146, which is charged either duringforward strokes of the power converter via the diode D3 or duringflyback (i.e., reverse) strokes of the power converter via diode D2.Powering capacitor 146 during forward strokes insures reliable start-up,even in the presence of a short-circuited output. Under normal operatingconditions, the capacitor 146 is charged only during forward strokes. Ifand when the output load goes to zero and the capacitor voltage falls atleast a diode drop below the output voltage 136, the capacitor 146 willalso be charged by flyback strokes.

The demand pulse generator 144 produces demand pulses DP that, by way ofthe signal transformer T2, the pulse detector 120, and the switch driver122, cause the main switch 116 to turn on for a limited time for eachdemand pulse DP so as to transfer power from the primary side 110 to thesecondary side 130 via the power transformer T1.

When present, the synchronous rectification circuitry 148 receives, fromthe demand pulse generator 144, a voltage timing signal DPGV thatindicates when the demand pulse generator 144 is generating anotherdemand pulse DP. In response, the synchronous rectification circuitry148 opens switch S1 to avoid current flowing the wrong way throughswitch S1 when the main switch 116 is closed. When the main switch 116is opened, the synchronous rectification circuitry 148 closes switch S1,thereby eliminating the diode drop across the diode D1 and reducing theassociated power losses.

In alternative implementations of the power converter 100, the outputvoltage 136 can be resistively divided before being applied to the erroramplifier 142, with the reference voltage REF similarly reduced to alower voltage level.

FIG. 2 is a schematic circuit diagram of the demand pulse generator 144,the signal transformer T2, and the pulse detector 120 of FIG. 1 showingdetails for one possible implementation of the demand pulse generator144. As shown in FIG. 2, the feedback signal FB from the error amplifier142 of FIG. 1 is applied to the base of n-type (npn bipolar) transistorQ3. When the feedback signal FB is low, transistor Q3 is off, whichallows the local power supply V+(i.e., capacitor 146 of FIG. 1) tocharge the timing capacitor C1 via the timing resistor R1 untiltransistor Q1 begins to turn on, which pulls down on the junction DPGVbetween resistor R2 and capacitor C2, which pushes down the voltage atthe base of transistor Q2 through the action of capacitor C2, therebyturning on transistor Q2. If either transistor Q1 or Q2 begins to turnon, both transistors are turned on abruptly because current throughtransistor Q2 increases the base-to-emitter junction voltage of Q1, andvice versa. The abrupt turning on of both transistors lasts only untilthe voltage between the collector of Q1 and the collector of Q2 falls tonear zero volts, at which time there is insufficient voltage present tokeep either transistor on. Both transistors remain off until there isenough voltage between the base of transistor Q1 and the base oftransistor Q2 to restart the process. With transistors Q1 and Q2 on, thecapacitive energy in capacitor C1 is rapidly drained by the currentthrough transistors Q1 and Q2 as DPGV drops abruptly to near zero volts.Note that, although a small amount of current continues to flow throughresistor R1 from the local power supply V+, the low impedance paththrough transistors Q1 and Q2 and the transformer winding 134 violentlydischarges the capacitor C1, overwhelming the charging from resistor R1.The resulting abrupt current passes through the primary winding 134 ofthe signal transformer T2, producing a demand pulse DP. Catch diode D4will then conduct, absorbing the voltage spike caused by the inductanceof the primary winding 134 of transformer T2. Catch diode D4 can beplaced on either side of transformer T2, or the inductive recoverycurrent can be limited with a snubber, as is known in the art.

Once capacitor C1 is drained and DPGV is near zero volts, there is notsufficient voltage present to keep either transistor Q1 or Q2 in the onstate, so capacitor C1 begins to charge again through resistor R1, andthe voltage at DPGV rises due to the pull-up action of resistor R2. Therising DPGV voltage at capacitor C2 causes the base of transistor Q2 torise, insuring that it remains off. Capacitor C2 provides positivefeedback for faster switching during both the positive and the negativetransitions. As used herein, the term “positive feedback” refers tofeedback that speeds transitions within circuitry, such as the turningon or off of transistors within the circuitry, as well as feedback thatspeeds transitions in the output signals generated by that circuitry,such as the pulses generated by a pulse generator, thereby shorteningthe rise and/or fall times of those pulses.

As long as the feedback signal FB is sufficiently low such that the npntransistor Q3 does not prevent charging of capacitor C1, the demandpulse generator 144 will continue to oscillate and generate demandpulses DP, each of which causes the main switch 116 of FIG. 1 to turnon, thereby transferring more power from the primary side 110 to thesecondary side 130 via the power transformer T1 and causing the outputvoltage 136 to rise. As the output voltage 136 rises towards thereference voltage REF, the feedback signal FB also rises, which startsto turn on the n-type transistor Q3, which in turn draws current andslows down the charging of the timing capacitor C1, thereby slowing downthe frequency of oscillation of the demand pulse generator 144 andtherefore the frequency of generation of the demand pulses DP. If andwhen the feedback signal FB is high enough to turn on transistor Q3sufficiently to stop charging of capacitor C1 (e.g., when the outputvoltage 136 reaches or exceeds the reference voltage REF), capacitor C1never sufficiently charges, n-type transistor Q1 never turns on, anddemand pulses DP are not generated.

As shown in FIG. 3, which is described further below, the negative edgesof the timing signal DPGV are synchronized with the demand pulses. Thetiming signal DPGV is helpful, though not essential, as an input to theoptional synchronous rectification circuitry 148 of FIG. 1, because DPGVprovides an indication just before the turning on of the main switch116. Instead of explicitly sensing that the main switch 116 has beenturned on, the DPGV signal allows the synchronous rectificationcircuitry 148 to insure that switch S1 of FIG. 1 is off a fewnanoseconds in advance of the main switch 116 turning on. The efficiencyof the synchronous rectifier would be ruined if switch S1 and the mainswitch 116 were on at the same time, even for a few nanoseconds, becausecurrent in switch S1 would then flow in the wrong direction.

To reduce power consumption, the energy that is accumulated in thetiming capacitor C1 is also used to energize the signal transformer T2when generating a demand pulse DP. Resistor R1 admits a tiny currentfrom the local power supply V+ to charge timing capacitor C1 which rampsup in voltage. Transistors Q1 and Q2 are in series with the primarywinding 134 of the signal transformer T2. The demand pulse generator 144includes positive feedback for fast action both when turning on and whenturning off the pulse current. When timing capacitor C1 charges to twoturn-on threshold voltages above the voltage at the base of Q2, bothtransistors Q1 and Q2 turn on abruptly. As used herein, the term“turn-on threshold voltage” refers to a voltage at which the transistorturns on. For bipolar transistors, the turn-on threshold voltage is thebase-to-emitter voltage at which the transistor begins to turn on. Forfield-effect transistors, the turn-on threshold voltage is thegate-to-source voltage at which the transistor begins to turn on.

Capacitor C2 provides positive feedback to insure both transistors arefully on. The sudden current continues until node DPGV is near groundpotential, at which time the two transistors Q1 and Q2 have no voltageacross them and can draw no current. There is then insufficient voltagepresent to reach the turn-on threshold voltages, so the two transistorsQ1 and Q2 turn off, resistor R2 begins to pull node DPGV back up towardthe local power supply voltage V+. Positive-feedback capacitor C2 nowcouples that upward shift to the base of transistor Q2, insuring that nocurrent will flow in transistors Q1 and Q2, thereby allowing timingcapacitor C1 to resume charging. The process then repeats.

If transistor Q3 is turned on by a rising feedback signal FB, whichindicates near or total sufficiency at the output node 136, then thetiming capacitor C1 will charge more slowly, or not at all, therebyretarding or stopping the generation of demand pulses DP.

The maximum pulse rate is determined by the time constant set by theratio of the timing resistor R1 to the timing capacitor C1. Thecapacitance values of capacitors C1 and C2 are the main determinants ofthe magnitude of the pulse current of the demand pulses DP. Thecomparator function provided by transistor Q3 requires a very low basecurrent and tolerates very slow rise and fall times. At low pulse ratescorresponding to low loads, the demand pulse generator 144 can operatewhile consuming under 100 microwatts. In general, power consumption forthe demand pulse generator 144 of FIGS. 1 and 2 can be less than 10% ofthe power consumption for equivalent PUT-based or SCS-based demand pulsegenerators.

The local power supply voltage V+ can be as low as a few volts or ashigh as the voltage ratings of the transistors. That flexibility caneliminate the need for a regulated supply to power the secondary side130 of the power converter 100 of FIG. 1. Also, since the demand pulsegenerator 144 can be designed to run at a local power supply voltage ofunder 5 volts, the demand pulse generator 144 can be powered through adiode connected to a regulated 5-volt output. In that case, the localpower supply would be needed only for startup, allowing the local powersupply to be completely shut down during normal operation for additionalpower savings. To implement that feature, a switch could be connected inseries with diode D3 in FIG. 1, where the switch would be closed if theoutput voltage 136 were too low and otherwise the switch would be open.

In the power converter 100 of FIGS. 1 and 2, the load for the demandpulse generator 144 is the inductive primary winding 134 of the signaltransformer T2. As described in further detail below, the circuitry usedto implement the demand pulse generator 144 in the isolated powerconverter 100 of FIGS. 1 and 2 can be used to implement a current pulsegenerator for other applications. If an application does not involveisolation, then the pulse generator load can be, but does not need to beinductive. The load can be resistive, or the load can be a diode or anyother suitable current-driven device.

Because large pulse currents are available at low power levels, thesignal transformer T2 need not have much inductance or very goodcoupling between the primary and secondary windings 134 and 118.Transformer winding inductance can be under 10 nH, and the couplingfactor K of the signal transformer T2 can be as low as 0.5. Thatflexibility allows size and cost savings for the galvanic isolation.

FIG. 3 shows simulated SPICE waveforms for the power converter 100 ofFIGS. 1 and 2. In the top trace, the output voltage 136 is seen risingto the regulation point, here 5 Volts. The demand pulses DP are seen inthe middle trace, where each demand pulse is represented as a briefnegative current pulse. From time 2.6 ms until about time 3.0 ms, thedemand pulses DP are generated at the maximum allowed rate as the outputvoltage 136 rises. As the output voltage 136 nears the regulation point,the rate of demand pulses DP slows from time 3.0 ms to time 3.2 ms. Atthe regulation point, after time 3.2 ms, the demand pulses DP occur at aconstant rate so as to support a constant load.

The bottom trace shows the voltage at the junction of resistor R2 andcapacitor C2 of FIG. 2 at node DPGV. When the demand pulse generator 144triggers (i.e., generates a single demand pulse DP), the DPGV voltagedrops quickly to near zero volts. Between triggers, the DPVG voltagerises toward the local power supply voltage V+ because of the current inpull-up resistor R2. The local power supply is unregulated in thisexample, so the local power supply voltage V+ also rises when theregulation point is reached because the demand pulse generator 144 loadsthe local power supply more lightly. Note that the local power supplyvoltage V+ is substantially equivalent to the DPGV waveform shown inFIG. 3, but without the downward spikes.

FIG. 4 is a schematic circuit diagram of the demand pulse generator 144,the signal transformer T2, and the pulse detector 120 of FIG. 1 showingdetails for another possible implementation of the demand pulsegenerator 144. The circuit of FIG. 4 is identical to the circuit of FIG.2 with three exceptions: npn transistor Q1 has been replaced by nmos FETM1, pnp transistor Q2 has been replaced with pmos FET M2, and diode D5has been added. The FETs M1 and M2 perform the functions of the bipolartransistors Q1 and Q2, and the circuit operates in the same fashion asthe circuit of FIG. 2. Diode D5 provides a path for discharging timingcapacitor C1 (along with transistors M1 and M2 and primary winding 134)when the demand pulse generator 144 triggers. Note that any combinationof FETs and bipolar transistors can be used to make a circuit withequivalent function to the circuit of FIG. 2.

The catch diode D4 of FIGS. 2 and 4 catches the recovery current thatrestores the inductive transformer winding 134. If that current is notcaught on the secondary side 130 of the power converter 100, then arecovery pulse will show up on the primary-side transformer winding 118in the opposite polarity from the demand pulse. Adding an additionalswitch in series with the catch diode D4 across the primary winding ofT2 in the demand pulse generator 144 provides a means for auxiliarydigital signaling, which would not alter the basic function of thedemand pulse generator 144.

FIG. 5A is a schematic circuit diagram of the demand pulse generator144, the signal transformer T2, and the pulse detector 120 of FIG. 1showing details for yet another possible implementation of the demandpulse generator 144. The circuit of FIG. 5A is identical to the circuitof FIG. 2 with the following exceptions: (i) the addition of switch S2in series with diode D4 and (ii) the addition of data state detector 124on the primary side of the signal transformer T2 which catches therecovery current. These additional elements provide a one-bitcommunication channel having a data rate equal to the pulse rate. Anysort of user-defined digital information could be transmitted from thesecondary side to the primary side by modulating the switch S2 using thedata signal DATA IN. If switch S2 is opened, then recovery current willflow on the primary side at the trailing edge of a demand pulse DP. Thatrecovery current can be detected by the data state detector 124. Ifswitch S2 is closed, then recovery current will flow in D4 on thesecondary side, and no recovery current will be detected by data statedetector 124.

Such auxiliary digital signaling could be used to send information fromthe secondary side 130 of the power converter 100 of FIG. 1 to theswitch driver 122 so as to modify its behavior. In variousimplementations, this additional information could be used, for example,as an over-temperature warning or to select between USB-PD and QuickCharge™ optimization.

FIG. 5B shows simulated waveforms for the modified demand pulsegenerator 144 of FIG. 5A. The top trace DATA IN is an arbitrary seriesof digital ones and zeros. The middle trace DBO is the output of thedata state detector 124 on the primary side. The lower trace DPO is theoutput of the demand pulse detector 120 on the primary side. It can beseen that, whenever the digital DATA IN is low (and switch S2 is open),the demand pulses are accompanied by DBO pulses. Whenever the digitalDATA IN is high (and switch S2 is closed), there are no DBO pulses.Thus, if a DPO demand pulse is detected on the primary side that is notaccompanied by a DBO pulse, then the state of DATA IN is known to behigh on the primary side. On the other hand, if a DPO demand pulse isaccompanied by a DBP pulse, then the state of DATA IN is known to be lowon the primary side.

Although the invention has been described so far in the context ofcurrent pulse generators for generating demand pulses for powerconverters that employ demand pulse regulation, the invention is not solimited. In general, the invention can be implemented to provide currentpulse generators for other suitable applications. Those applicationsinclude any comparator function requiring a fast output edge in responseto a slow input with low power consumption. IoT devices andbattery-powered electronics such as implantable medical devices are goodcandidates.

FIG. 6A is a generalized schematic circuit diagram of a circuit 600according to certain embodiments of the invention. Depending on how thecircuit 600 is controlled, it can operate as a current pulse generatoranalogous to the demand pulse generators of FIGS. 2 and 4-5 (althoughthe circuit 600 can be used as a current pulse generator in applicationsother than an isolated power converter), as a form of one shot, or as atime-delay circuit. Using the triggering approach of FIG. 6A, analogtime-delay circuits can exhibit the crisp and repeatable performancepreviously seen only with digital time-delay circuitry. The circuit 600has the same basic elements (i.e., n-type transistor Q1, p-typetransistor Q2, timing resistor R1, timing capacitor C1,positive-feedback capacitor C2, and resistors R2-R3) as the demand pulsegenerator 144 of FIG. 2. In addition to the control port A, of which thecollector of n-type transistor Q3 of FIG. 2 is an example, the circuit600 has additional or alternative control ports B and C that can be usedto control the operations of the circuit 600.

FIG. 6A be modified and adapted in a variety of ways. Current can beinjected or removed from almost any node in the circuit to influence thefrequency of oscillation or the magnitude of the pulse current, or tostop oscillation entirely. The symmetry of the circuit allows eithercapacitor C1 or C2 to act as the timing capacitor, and either or bothcan act as positive-feedback capacitors. The particular values selectedfor the resistors and capacitors will determine the range of frequenciesand currents available and the start-up behavior, which can be acritical factor in the practicality of oscillating circuits. Anoscillator should start predictably to be reliable, and should not drawexcessive current during start up. The circuit of FIG. 6A provides abasis for providing all of these advantages.

FIG. 6B shows simulated waveforms for the circuit 600 of FIG. 6Aoperating as a gated, voltage-controlled oscillator. The control voltage604 is applied at control port B. The feedback voltage FB is used togate the oscillator. When FB is low, transistor Q3 is off, which allowsthe circuit 600 to oscillate and generate current pulses I through themain load position 610 or the alternative load position 612. When FB ishigh, transistor Q3 is on, thereby holding the voltage 602 at capacitorC1 low, so that oscillation stops. The frequency of oscillation ismodulated by the voltage 604 at control port B. The voltage 602 atcontrol port A needs to rise to two turn-on threshold voltages above thevoltage at the control port B in order to trigger the pulse output I.Since control port A is reset to near zero volts each time the circuit600 triggers, the control voltage 602 has further to rise in order toreach the trigger point as control voltage 604 goes up. The extra timerequired for the additional charging at control port A increases theperiod and decreases the frequency of oscillation. When the controlvoltage 604 is near its maximum, only one current pulse I occurs duringthe enable time provided by the gating signal FB. If control voltage 604were to rise above two threshold drops below the local power supplyvoltage 6Q, the oscillation would stop, regardless of the state of FB.

This type of voltage-controlled oscillator provides several advantagesover conventional circuits. The oscillating circuit 600 runs over a widepower supply voltage range, and starts reliably and predictably. Powerconsumption can be micro watts, and the fast edge at triggering providesprecise timing.

FIG. 6C shows simulated SPICE waveforms for the circuit 600 of FIG. 6Aoperating as a variable delay generator. The control voltage 604 atcontrol port B ramps up and down in similar fashion to FIG. 6B. Thesignal FB is applied to the base of transistor Q3 through a resistor toenable the signal FB to rise to the local power supply voltage V+.Control voltage 606 applied at control port C through a diode isidentical to the FB voltage and arms the circuit 600 for triggering.When FB and control voltage 606 are high, the trigger is armed but thetiming capacitor C1 cannot charge because transistor Q3 is held on byFB. When FB falls, C1 begins to charge. When the voltage 602 at controlnode A reaches a voltage two threshold drops above the voltage 604 atcontrol node B the circuit 600 triggers, producing a current pulse I anda fast voltage edge at the output port 608, where the delay between thefalling edge of FB and the current pulse I is directly related to themagnitude of the control voltage 604 at control port B. The output port608 will stay low, and no more pulses will be generated until thecircuit 600 is re-armed by control voltage 606 rising again. As in FIG.6B, the delay time is set by the voltage 604 at control port B over arange that is determined by resistor and capacitor values.

If a switchable current source is used in place of resistor R1 andtransistor Q3 to control the charging of capacitor C1, then the armedbut untriggered current can approach zero. The unarmed current can alsoapproach zero. With almost no input power, the trigger of FIG. 6Cgenerates very fast output pulses even with a slowly changing signal 602at control port A. A circuit producing a digital output signal with arelatively fast edge in response to a slowly changing analog or digitalinput signal can be characterized as an edge accelerator. The edgeaccelerator taught here has the advantage of very low input power.

In addition to the main load position 610, of which the primary winding134 of FIG. 2 is an example, the circuit 600 has an alternative loadposition 612 below both transistors Q1 and Q2 at which output currentpulses can appear. Under some circumstances, it may be convenient tohave a ground-referenced load at the alternative load position 612.Moving the load to the alternative load position 612 does not change thefundamental circuit behavior. At either load position 610 or 612, thenature of the load does not need to be inductive for the operation ofthe circuit 600. It would also be possible to place a load in serieswith the collector of transformer Q1. Possible loads include, but arenot limited to, laser or light-emitting diodes, gate drivers forsolid-state switches, triac or SCR (silicon controlled rectifier)triggering circuits, strobe lights, or sound-generating transducers. Theoutput pulse at the load position 610 or 612 could also be applieddirectly to the primary winding of a power transformer.

Different types of control signals can be applied to the control ports Aand B singly or in combination to modify the behavior of the circuit 600in different ways. Control possibilities include changing the maximumoperating frequency, slowing, speeding, or stopping pulse generation,varying the magnitude of the pulsed current, and, within certain narrowlimits, varying the pulse width.

For example, if no current is applied to the control port A, then (i)the timing capacitor C1 will charge at a free-running time constantbased on the timing capacitor C1 and the timing resistor R1 and (ii) thecircuit 600 will generate current pulses flowing through the main loadposition 610 and the alternative load position 612 at a free-runningfrequency of the circuit 600.

If, instead, a moderate sink current is applied to the control port A,then (i) the timing capacitor C1 will charge at a time constant longerthan the free-running time constant and (ii) the circuit 600 willgenerate current pulses at a frequency lower than the free-runningfrequency. If a sufficiently high sink current is applied to the controlport A, then (i) the timing capacitor C1 will not charge to a thresholdlevel sufficient to turn on transistor Q1 and (ii) the circuit 600 willstop generating current pulses. Note that the n-type transistor Q3 ofFIG. 2 is capable of controlling the frequency of current pulses fromzero (when Q3 is more strongly on) to the free-running frequency (whenQ3 is off).

If, instead of a sink current, a source current is applied to thecontrol port A, then (i) the timing capacitor C1 will charge at a timeconstant shorter than the free-running time constant and (ii) thecircuit 600 will generate current pulses at a frequency higher than thefree-running frequency. This function can be achieved by connecting andappropriately controlling a (p-type or n-type) transistor between thecontrol port A and the power supply V+ either instead of or in additionto the transistor Q3. With a current source applied to capacitor C1,resistor R1 can be omitted, so that the charging of C1 is entirelydetermined by the current source.

As described previously with respect to the pulse generator of FIG. 6A,an appropriate positive voltage signal can be applied at the controlport B of FIG. 6A to prevent transistor Q2 from turning on in order toprevent the circuit 600 from generated current pulses. In general,influencing the voltage at control port B changes the trigger thresholdfor control port A. Raising or lowering that trigger threshold can alterthe frequency with which the circuit 600 generates current pulses,including completely stopping the generation of current pulses. When thecircuit 600 is operated as a one shot, the DC triggering level isestablished at control port B.

By using power transistors for the switching elements Q1 and Q2 in FIG.6A, arbitrarily large amounts of power can be pulsed efficiently forapplications that require periodic, high-power current pulses, such asrange finders and medical imaging systems.

FIG. 7 is a generalized schematic circuit diagram of a circuit 700according to certain other embodiments of the invention. Instead of thevoltage output 608 being tied to the positive power supply rail V+ viaresistor R2 as in the circuit 600 of FIG. 6A, in the circuit 700 of FIG.7, the voltage output 708 is tied to the negative power supply rail V−(e.g., ground) via resistor R4. As such, the circuit 700 is an inversionof the circuit 600 of FIG. 6A. In particular, the output voltage 708 nowbecomes a positive-going voltage when the circuit 700 triggers, insteadof the negative-going output voltage 608 of FIG. 6A (e.g., the timingsignal DPGV in FIGS. 2 and 3). The output current pulse (at either loadposition 710 or 712) is essentially identical to the correspondingoutput current pulse generated by the circuit 600 of FIG. 6A. Thealternative positions for the load 710 and 712 and for the control portsA-D correspond to the alternative positions shown in FIG. 6A.

In FIG. 7, capacitors C1 and C2 can exchange functions compared to FIG.6A, depending on the control inputs. Alternatively, capacitor C1 or C2could be replaced by a resistor for monostable operation such as isshown in FIGS. 9, 10, and 12. In addition, FETS can replace either orboth bipolar transistors.

Possible sources for the control signals applied at the control ports Aand B for the circuit 700 of FIG. 7 include zero-crossing detectors andsensors for temperature, pressure, motion, light, ionization, andradiation, among others.

FIG. 8 is a generalized schematic circuit diagram of a circuit 800according to certain other embodiments of the invention. Instead ofbeing charged via the timing resistor R1 of FIG. 6A, the timingcapacitor C1 is charged from a current source 814 controlled at controlport C. The charging by the current source 814 linearizes the risingvoltage on the timing capacitor C1, thereby enabling more-accuratetiming. The current source 814 can be modulated or turned completely offat the control port C.

Instead of robbing charging current through transistor Q3 of FIG. 2, tostop the generation of pulses, when the charging current from thecurrent source 814 is shut off at the control port C, the minimum powerrequired by the circuit 800 can drop to near zero. In order to set a DCoperating point for the base of transistor Q2 under those steady-stateconditions, a bias resistor R5 has been added in FIG. 8. The biasresistor R5 will draw current even when there are no pulses beinggenerated, but that current can be vanishingly small.

With some or all of these refinements, the circuit 800 can operate overan extremely wide range of frequencies, from sub one Hertz rates to over10 Megahertz using ordinary transistors, all while consuming a fractionof the power required by prior-art pulse generators.

A signal transformer is intrinsically bidirectional. The secondarywinding of the signal transformer T2 could be the load in a seconddemand pulse generator. Then, pulse detectors could operate on bothwindings of transformer T2, one on each side of the isolation barrier.In this fashion, the pulse generator could be made bidirectional. Thatcapability could be useful for a bidirectional power converter or forother isolated circuits.

It will be evident to those skilled in the art that other versions ofthe pulse generator are possible. Current direction or voltage polaritycan be reversed, possibly including the exchange of n-type for p-typeswitching devices and vice versa. For even faster switching, GAAS, GaN,SiC, or other high electron mobility transistor (HEMT) switches can besubstituted. A positive and a negative version of the pulse generatorcould be paired, responding hysteretically to the same input signal toform a fast-acting, ultra-low-power logic buffer.

FIG. 9 is a schematic circuit diagram of a hysteretic buffer 900 formedfrom a complementary pair of pulse generators 910 and 920, according tocertain embodiments of the invention. In low-power circuitry, a slowlychanging signal falling between a logic high level and a logic low leveland connected to a logic input will cause currents to be drawn far inexcess of currents drawn when an input is at a logic high or logic lowlevel. In a power converter, such slowly changing signals could, forexample, include comparator outputs or error amplifier outputs. Withlow-power, limited-bandwidth circuits, such signals tend to spendconsiderable time in transition. Those slow transitions waste power inlogic circuitry. Similar inefficiencies are an issue in other devices,including battery-powered devices, IoT devices, and always-on standbycircuits in computers, TVs, appliances, etc.

The buffer 900 of FIG. 9 draws only a small current even as the inputvoltage 902 approaches a threshold point. When the buffer 900 switchesstate, the state transitions rapidly, so that downstream logic canoperate more efficiently. The hysteretic buffer 900 might have threeregions of operation: zero to ⅓ of the power supply voltage 9D(corresponding to logic low), ⅓ to ⅔ of the power supply voltage(corresponding to an indeterminate logic state), and above ⅔ of thepower supply voltage (corresponding to logic high). The buffer 900 isinverting, though non-inverting forms will be apparent to those skilledin the art.

The upper half 910 of the buffer 900 is a version of the generalizedcircuit 600 of FIG. 6A, where elements Q10, Q11, R10, R12, R13, and C12of FIG. 9 are respectively analogous to elements Q1, Q2, R1, R2, R3, andC2 of FIG. 6A. The upper half 910 is triggered by the input 902 fallingbelow a threshold voltage, in this example, approximately ⅓ of thesupply voltage 9D. When the upper half 910 is triggered, the output 9Dis pulled sharply upward by Q10 and Q11 as they generate a positivecurrent pulse.

The lower half 920 of the circuit (i.e., elements Q14, Q15, R15-R18, andC13) is a second circuit mirrored in complementary form, triggered bythe input 902 rising above a second threshold voltage, hereapproximately ⅔ of the supply voltage. The two halves 910 and 920,working in alternation, cause the output 904 to be an inverted digitalrepresentation of the input 902 with ⅓ of the power supply voltage ashysteresis. The buffer 900 of FIG. 9 draws a pulse of current at eachdigital edge of the output 904, but draws a minimum amount of currentwhile in either logic state, even while the input 902 is in theindeterminate middle ⅓ of the voltage range. By adjusting componentvalues, the trade-off between output slew rate and quiescent power canbe set as desired. For example, 1-microsecond transitions require about10 microwatts of quiescent power. The threshold voltages for thehysteretic operation can be set as desired by adjusting resistor ratios.

Resistors R12 and R13, in combination with resistors R10 and R14, set athreshold voltage for the positive-going output edge. Capacitor C12provides positive feedback to speed the positive edge. Resistors R15 andR16, in combination with resistors R17 and R18, set a threshold voltagefor the negative-going output edge. Capacitor C13 provides positivefeedback to speed the negative edge. Just a few picofarads ofcapacitance is necessary, so the capacitors C12 and C13 can be builtinto an integrated circuit. The lower half 920 of the buffer 900 pullsdown hard when the input 902 rises above the positive-going thresholdvoltage.

FIG. 10 is a schematic circuit diagram of a hysteretic buffer 1000according to certain other embodiments of the invention. Buffer 1000 isthe same as buffer 900 of FIG. 9 with the addition of an optional inputbuffer 1030 comprising complementary bipolar transistors Q16 and Q17 andan optional output buffer 1040 comprising complementary FET transistors1042 and 1044. Note that the two input transistors Q16 and Q17 could beFETs for even lower input currents. The emitters of the two transistorsQ16 and Q17 can be connected to different points in the resistivedivider formed by resistors R12, R13, R15, and R16 to provide additionalfreedom when selecting hysteretic threshold voltages. Also, thecomplementary pulse generators 910/920 and 1010/1020 in FIGS. 9 and 10,respectively, could be made with FETs instead of bipolar transistors, asin FIG. 4, if FETs are preferred. Optional input buffer 1030 and/oroptional output buffer 1040 can be added to increase input impedance orreduce output impedance, as desired.

FIG. 11 shows simulated SPICE waveforms for a medium speed version ofthe hysteretic buffer 900 of FIG. 9 for upper and lower voltage rails at5V and 0V, respectively. The upper graph shows power drawn by the buffer900, and the lower graph shows the input and output voltages 902 and904. In this particular example, the input voltage 902 is a 1 Hertztriangle wave that dwells most of the time between the upper and lowerthreshold voltages of approximately 3.3V and 1.7V, respectively. Theoutput voltage 904 is a logic level with about 26-nanosecond transitiontimes. At 0.45 seconds elapsed time, the input voltage 902 rises abovethe 3.3V upper threshold voltage, triggering a negative current pulse(represented by power spike 1102), in turn causing a negative transitionin the output voltage 904. At 0.95 seconds elapsed time, the inputvoltage 902 falls below the 1.7V lower threshold voltage, triggering apositive current pulse (represented by power spike 1104), which causes apositive transition in the output voltage 904. Again, the hysteresisthreshold voltages can be set as desired by changing resistor ratios,and the switching speed can be controlled by changing total impedancesor by changing capacitor values. Some minimum amount of hysteresisprevents both pulse generators 910 and 920 from acting simultaneously,which would cause excess current to flow.

The average power drawn in this example is about 860 microwatts. Thepulses generated by the actions of the two complementary pulsegenerators 910 and 920 correspond to the power spikes 1102-1108 shown inthe upper trace of FIG. 11. With higher-impedance resistors, the averagepower drawn can be reduced below 10 microwatts while still achieving1-microsecond output transitions. At higher average power, transitionsof a few nanoseconds are possible.

Two instances of the hysteretic inverting buffer 900 can be connected inseries to form a non-inverting buffer. That arrangement entails a smallamount of additional delay from input to output, but such delay rarelyis of concern in circuits with very slowly changing inputs. The outputof the second inverting buffer will transition even faster in thenon-inverting form, so the extra power consumed by the second buffer maybe more than saved through the reduction of power consumed by downstreamdigital circuitry.

Alternatively, the second inversion could be provided by a power driverstage suitable for directly driving power FETs or other solid stateswitches. Such an output stage is shown as optional output buffer 1040in FIG. 10. That arrangement could reduce switching losses by minimizingtime spent in transition between on and off, or off and on. As known inthe art, a buffer outputs relatively low-power logic levels fordownstream digital circuitry, while the output generated by a powerdriver stage would typically have orders of magnitude more current.

FIG. 12 shows an alternative input structure 1230 for a hystereticbuffer 1200. Resistors R19 and R20, in combination with capacitor C14,induce a slight delay in the response at the bases of the transistorsQ11 and Q14. That delay insures that the transistor pair Q11 and Q14turns all the way off, instead of tending toward a linear operatingpoint

One application of the buffers of FIG. 9, 10, or 12 would be tocondition the clock input of a clocked bistable. These devices, asgenerally provided, specify a maximum clock transition time.Indeterminate behavior can occur with slower clock edges. In addition,slow clock edges drastically increase the power consumption. With theaddition of the buffer 1000 of FIG. 10 on the clock input, the bistablecan operate properly and efficiently with arbitrarily long clocktransition times. If only one clock edge is critical, then an edgeaccelerator based on a single trigger circuit such as shown in FIG. 6A,7, or 8 might suffice.

The power converter 100 of FIG. 1 can be implemented using twointegrated circuits: a primary-side die that implements the circuitry onthe primary side 110 of the power and signal transformers T1 and T2 anda secondary-side die that implements the circuitry on the secondary side130 of the power and signal transformers T1 and T2. The transformers T1and T2 can be implemented using discrete elements. In someimplementations, the signal transformer can be implemented using leadframe structure as described in U.S. Pat. No. 8,818,296, the teachingsof which are incorporated herein by reference. In some implementations,diode D1 and/or switch S1 (if present) might also be implemented asdiscrete elements. In some implementations, the secondary-side die canimplement additional, digital circuitry, for example, to modify thebehavior of the power converter according to USB-PD or Quick Charge™protocols. In some alternative embodiments, as taught in the '152patent, a single transformer functions as both the power and signaltransformers T1 and T2.

The circuits of FIGS. 2 and 4-10 provide different circuit-levelfunctions. As described previously, the circuits 144 of FIGS. 2 and 4-5can be controlled to operate as demand pulse generators in isolatedpower converters, the circuits 600, 700, and 800 of FIGS. 6, 7, and 8can be controlled to operate as either oscillating current pulsegenerators or as trigger devices, and the circuits 900 and 1000 of FIGS.9 and 10 can be controlled to operate as hysteretic buffers. What all ofthese different circuits have in common is trigger circuitry comprising(i) two series-connected transistors of opposite type that turn ontogether when the voltage at the base/gate of the n-type device exceedsthe voltage at the base/gate of the p-type device by at least the sum ofthe turn-on threshold voltages of the two transistors. The transistorsturn off together when the voltage across the two transistors drops and(ii) a positive-feedback capacitor that ensures that the two transistorsturn on and off together quickly and securely.

Referring to the demand pulse generator 144 of FIG. 2, the triggercircuitry comprises the n-type transistor Q1, the p-type transistor Q2,and the positive-feedback capacitor C2. The collector and emitter of thetransistor Q1 are connected in series with the collector and emitter ofthe transistor Q2 such that, when the two transistors are turned on,current flows from the emitter of the n-type transistor Q1 to theemitter of the p-type transistor Q2. The positive-feedback capacitor C2is connected between the collector of the n-type transistor Q1 and thebase of the p-type transistor Q2. The two transistors are turned on whenthe voltage at the base of the n-type transistor Q1 exceeds the voltageat the base of the p-type transistor Q2 by at least the sum of theturn-on threshold voltages of the two transistors. The voltage acrossthe positive-feedback capacitor C2 ensures that both transistors areturned on quickly and securely. When the two transistors are triggered,the current flowing from the collector of transistor Q1 to the collectorof transistor Q2 quickly drains the timing capacitor C1 and causes thevoltage at the base of the n-type transistor Q1 not to exceed thevoltage at the base of the p-type transistor Q2 by at least the sum ofthe turn-on threshold voltages of the two transistors, which causes thetwo transistors Q1 and Q2 to turn off together. Here, too, the voltageacross the positive-feedback capacitor C2 ensures that both transistorsQ1 and Q2 are turned off quickly and securely.

The analogous trigger circuitry of transistors Q1 and Q2 andpositive-feedback capacitor C2 in each of circuits of FIGS. 6-8 can besimilarly described. The corresponding trigger circuitry in each of thecircuits of FIGS. 4-5 can be analogously described, albeit for the FETtransistors M1 and M2 instead of the bipolar transistors Q1 and Q2 ofFIG. 2.

The hysteretic buffers of FIGS. 9 and 10 have two sets of triggercircuitry: a first set comprising transistors Q10 and Q11 and capacitorC12 and a second set comprising transistors Q14 and Q15 and capacitorC13. For the first set of trigger circuitry, the collector and emitterof the transistor Q10 are connected in series with the collector andemitter of the transistor Q11 such that, when the two transistors areturned on, current flows from the emitter of the n-type transistor Q10to the emitter of the p-type transistor Q11. The positive-feedbackcapacitor C12 is connected between the collector of the p-typetransistor Q11 and the base of the n-type transistor Q10. The twotransistors are turned on when the voltage at the base of the n-typetransistor Q10 exceeds the voltage at the base of the p-type transistorQ11 by at least the sum of the turn-on threshold voltages of the twotransistors. The voltage across the positive-feedback capacitor C12ensures that both transistors are turned on quickly and securely. Whenthe two transistors are triggered, current flows from the collector oftransistor Q10 to the collector of transistor Q11, which causes thevoltage at the base of the n-type transistor Q10 not to exceed thevoltage at the base of the p-type transistor Q11 by at least the sum ofthe turn-on threshold voltages of the two transistors, which causes thetwo transistors Q10 and Q11 to turn off together. Here, the voltageacross the positive-feedback capacitor C12 ensures that both transistorsQ10 and Q11 are turned off quickly and securely.

For the second set of trigger circuitry of FIGS. 9 and 10, the collectorand emitter of the transistor Q14 are connected in series with thecollector and emitter of the transistor Q15 such that, when the twotransistors are turned on, current flows from the emitter of the n-typetransistor Q14 to the emitter of the p-type transistor Q15. Thepositive-feedback capacitor C13 is connected between the collector ofthe n-type transistor Q14 and the base of the p-type transistor Q15. Thetwo transistors are turned on when the voltage at the base of the n-typetransistor Q14 exceeds the voltage at the base of the p-type transistorQ15 by at least the sum of the turn-on threshold voltages of the twotransistors. The voltage across the positive-feedback capacitor C13ensures that both transistors are turned on quickly and securely. Whenthe two transistors are triggered, current flows from the collector oftransistor Q14 to the collector of transistor Q15, which causes thevoltage at the base of the n-type transistor Q14 not to exceed thevoltage at the base of the p-type transistor Q15 by at least the sum ofthe turn-on threshold voltages of the two transistors, which causes thetwo transistors Q14 and Q15 to turn off together. Here, the voltageacross the positive-feedback capacitor C13 ensures that both transistorsQ14 and Q15 are turned off quickly and securely.

In certain embodiments, circuitry comprises a trigger circuit. Thetrigger circuit comprises an n-type transistor (e.g., Q1, Q10, Q14)having a base, a collector, and an emitter and characterized by aturn-on threshold voltage; a p-type transistor (e.g., Q2, Q12, Q15)having a base, a collector, and an emitter and characterized by aturn-on threshold voltage, wherein the collector and emitter of then-type transistor are connected in series with the collector and emitterof the p-type transistor such that, when the two transistors are turnedon, current flows from the collector of the n-type transistor to thecollector of the p-type transistor; and a positive-feedback capacitor(e.g., C1, C2, C12, C13) connected between the collector of a first(e.g., Q2, Q1, Q11, Q14) of the two transistors and the base of a second(e.g., Q1, Q2, Q10, Q15) of the two transistors. The trigger circuit isconfigured such that (i) the two transistors turn on together when thevoltage at the base of the n-type transistor exceeds the voltage at thebase of the p-type transistor by at least the sum of the turn-onthreshold voltages of the two transistors and (i) the two transistorsturn off together when the voltage at the base of the n-type transistorfails to exceed the voltage at the base of the p-type transistor by atleast the sum of the turn-on threshold voltages of the two transistors.The positive-feedback capacitor ensures that the two transistors turnfully on and off together.

In certain embodiments of the foregoing, the two transistors are bipolartransistors (e.g., Q1/Q2, Q10/Q11, Q14/Q15) or field-effect transistors(e.g., M1/M2).

In certain embodiments of the foregoing, the first transistor is then-type transistor (e.g., Q1, M1, Q14); the second transistor is thep-type transistor (e.g., Q2, M2, Q15); and the positive-feedbackcapacitor (e.g., C2, C13) is connected between the collector of then-type transistor and the base of the p-type transistor.

In certain embodiments of the foregoing, the circuitry further comprisesa timing capacitor (e.g., C1) connected to the base of the n-typetransistor and configured to be charged when the two transistors are offand discharged when the two transistors are on. The charging of thetiming capacitor causes the two transistors to turn on, and thedischarging of the timing capacitor contributes to a current pulsethrough the two transistors.

In certain embodiments of the foregoing, the first transistor is thep-type transistor (e.g., Q2, Q11); the second transistor is the n-typetransistor (e.g., Q1, Q10); and the positive-feedback capacitor (e.g.,C1, C12) is connected between the collector of the p-type transistor andthe base of the n-type transistor.

In certain embodiments of the foregoing, wherein the circuitry furthercomprises a timing capacitor (e.g., C2) connected to the base of thep-type transistor (e.g., Q2) and configured to be charged when the twotransistors are off and discharged when the two transistors are on. Thecharging of the timing capacitor causes the two transistors to turn on,and the discharging of the timing capacitor contributes to a currentpulse through the two transistors.

In certain embodiments of the foregoing, an output load (e.g., 610) isconnected in series between the emitter of the n-type transistor and theemitter of the p-type transistor.

In certain embodiments of the foregoing, the output load comprises atransformer winding (e.g., 134).

In certain embodiments of the foregoing, the output load furthercomprises a switch (e.g., S2) connected in series with a catch diode(e.g., D4); the switch and the catch diode are connected in parallelwith the transformer winding; and the switch is configured to beselectively controlled to transmit data via the transformer winding.

In certain embodiments of the foregoing, an output load (e.g., 612) isconnected in series between the collector of the p-type transistor and alow-voltage supply rail (e.g., V−) of the circuitry.

In certain embodiments of the foregoing, an output load is connected inseries between the collector of the n-type transistor and a high-voltagesupply rail (e.g., V+) of the circuitry.

In certain embodiments of the foregoing, the emitter of the n-typetransistor is directly connected to the emitter of the p-typetransistor.

In certain embodiments of the foregoing, the trigger circuit is part ofa pulse generator configured to generate current pulses corresponding tothe current flowing from the collector of the n-type transistor to thecollector of the p-type transistor.

In certain embodiments of the foregoing, the pulse generator is acontrolled pulse generator configured to receive a control signal thatcontrols frequency of the current pulses.

In certain embodiments of the foregoing, the pulse generator is a demandpulse generator (e.g., 144) on the secondary side of an isolated powerconverter.

In certain embodiments of the foregoing, the circuitry comprises theisolated power converter configurable to drive an output load.

In certain embodiments of the foregoing, the circuitry comprises theoutput load.

In certain embodiments of the foregoing, the trigger circuit is part ofan oscillator that oscillates with the two transistors repeatedlyturning on and off together.

In certain embodiments of the foregoing, the oscillator is a controlledoscillator configured to receive a control signal that controlsfrequency of the oscillation.

In certain embodiments of the foregoing, the trigger circuit is part ofa delay circuit that receives an input signal and generates a delayedoutput signal when the two transistors turn on together.

In certain embodiments of the foregoing, the delay circuit is acontrolled delay circuit configured to receive a control signal thatcontrols magnitude of the delay between the input signal and the delayedoutput signal.

In certain embodiments of the foregoing, the trigger circuit is part ofan edge accelerator that receives an input signal having an inputleading edge with an input transition time and generates, when the twotransistors turn on together, an output signal having an output leadingedge with an output transition time that is shorter than the inputtransition time.

In certain embodiments of the foregoing, the edge accelerator is abuffer (e.g., 900) comprising the trigger circuit (e.g., Q10, Q11, C12)connected in parallel with a complementary version of the triggercircuit (e.g., Q14, Q15, C13). When the buffer receives a first inputsignal, the two transistors (e.g., Q10/Q11) of the trigger circuit turnon together and the buffer generates an output signal having a firstlogical value. When the buffer receives a second input signal, the twotransistors (e.g., Q14/Q15) of the complementary version of the triggercircuit turn on together and the buffer generates the output signalhaving a second logical value.

Embodiments of the invention may be implemented as (analog, digital, ora hybrid of both analog and digital) circuit-based processes, includingpossible implementation as a single integrated circuit (such as an ASICor an FPGA), a multi-chip module, a single card, or a multi-card circuitpack.

Also for purposes of this description, the terms “couple,” “coupling,”“coupled,” “connect,” “connecting,” or “connected” refer to any mannerknown in the art or later developed in which energy is allowed to betransferred between two or more elements, and the interposition of oneor more additional elements is contemplated, although not required.Conversely, the terms “directly coupled,” “directly connected,” etc.,imply the absence of such additional elements.

Signals, voltages, or currents and corresponding terminals, nodes,ports, or paths may be referred to by the same name and areinterchangeable for purposes here.

Transistors are typically shown as single devices for illustrativepurposes. However, it is understood by those with skill in the art thattransistors will have various sizes (e.g., gate width and length) andcharacteristics (e.g., threshold voltage, gain, etc.) and may consist ofmultiple transistors coupled in parallel to get desired electricalcharacteristics from the combination. Further, the illustratedtransistors may be composite transistors.

As used in this specification and claims, the terms “emitter,”“collector,” and “base” should be understood to refer respectivelyeither to the emitter, collector, and base of a bi-polar device or tothe source, drain, and gate of a FET device if an embodiment of theinvention is implemented using FET transistor technology.

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word “about” or“approximately” preceded the value or range.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain embodiments of this invention may bemade by those skilled in the art without departing from embodiments ofthe invention encompassed by the following claims.

In this specification including any claims, the term “each” may be usedto refer to one or more specified characteristics of a plurality ofpreviously recited elements or steps. When used with the open-ended term“comprising,” the recitation of the term “each” does not excludeadditional, unrecited elements or steps. Thus, it will be understoodthat an apparatus may have additional, unrecited elements and a methodmay have additional, unrecited steps, where the additional, unrecitedelements or steps do not have the one or more specified characteristics.

All documents mentioned herein are hereby incorporated by reference intheir entirety or alternatively to provide the disclosure for which theywere specifically relied upon.

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments necessarilymutually exclusive of other embodiments. The same applies to the term“implementation.”

The use of figure numbers and/or figure reference labels in the claimsis intended to identify one or more possible embodiments of the claimedsubject matter in order to facilitate the interpretation of the claims.Such use is not to be construed as necessarily limiting the scope ofthose claims to the embodiments shown in the corresponding figures.

The embodiments covered by the claims in this application are limited toembodiments that (1) are enabled by this specification and (2)correspond to statutory subject matter. Non-enabled embodiments andembodiments that correspond to non-statutory subject matter areexplicitly disclaimed even if they fall within the scope of the claims.

Unless otherwise specified herein, the use of the ordinal adjectives“first,” “second,” “third,” etc., to refer to an object of a pluralityof like objects merely indicates that different instances of such likeobjects are being referred to, and is not intended to imply that thelike objects so referred-to have to be in a corresponding order orsequence, either temporally, spatially, in ranking, or in any othermanner.

What is claimed is:
 1. An article of manufacture comprising a flybackconverter, the flyback converter comprising: a primary side comprisingan input port; a secondary side comprising an output port, wherein thesecondary side is galvanically isolated from the primary side; and apower transformer configured to transfer input power received at theinput port to provide output power at the output port, wherein: theprimary side further comprises a primary-side switch configured toselectively enable the input power at the input port to be transferredvia the power transformer to the output power at the output port; thesecondary side further comprises a demand pulse generator that (i)determines when to turn on the primary-side switch based on outputvoltage or output current at the output port and (ii) generatescorresponding demand pulses; the primary side comprises a primary-sidemagnetically coupled conductor; the secondary side comprises asecondary-side magnetically coupled conductor configured to bemagnetically coupled to the primary-side magnetically coupled conductorto convey the demand pulses from the secondary side to the primary side;the primary-side switch is turned on in response to a demand pulseconveyed from the secondary side to the primary side; the demand pulsegenerator comprises: an n-type transistor having a base, a collector,and an emitter and characterized by a turn-on threshold voltage; ap-type transistor having a base, a collector, and an emitter andcharacterized by a turn-on threshold voltage, wherein the collector andemitter of the n-type transistor are connected in series with thecollector and emitter of the p-type transistor such that, when the twotransistors are turned on, current flows from the collector of then-type transistor to the collector of the p-type transistor; and apositive-feedback capacitor connected between the collector of a firstof the two transistors and the base of a second of the two transistors,wherein: the demand pulse generator is configured such that (i) the twotransistors turn on together when the voltage at the base of the n-typetransistor exceeds the voltage at the base of the p-type transistor byat least the sum of the turn-on threshold voltages of the twotransistors and (i) the two transistors turn off together when thevoltage at the base of the n-type transistor fails to exceed the voltageat the base of the p-type transistor by at least the sum of the turn-onthreshold voltages of the two transistors; and the positive-feedbackcapacitor ensures that the two transistors turn fully on and offtogether.
 2. The article of claim 1, wherein the primary side furthercomprises: a demand pulse detector connected to the primary-sidemagnetically coupled conductor; and a switch driver connected to thedemand pulse detector and the primary-side switch, wherein: the demandpulse detector detects a demand pulse transmitted from the secondaryside via the secondary- and primary-side magnetically coupled conductorsto the primary side; and the switch driver turns on the primary-sideswitch based on the detection of the demand pulse by the demand pulsedetector.
 3. The article of claim 1, wherein: when the output port is inregulation, the determination of when to turn off the primary-sideswitch is originated on the primary side; frequency with which theprimary-side switch is turned on is based on the demand pulses conveyedfrom the secondary side to the primary side to regulate the outputvoltage or the output current at the output port; and the demand pulsegenerator is at least partially powered using energy transferred to thesecondary side during forward power converter pulses of the flybackconverter.
 4. The article of claim 1, wherein the two transistors arebipolar transistors or field-effect transistors.
 5. The article of claim1, wherein: the first transistor is the n-type transistor; the secondtransistor is the p-type transistor; and the positive-feedback capacitoris connected between the collector of the n-type transistor and the baseof the p-type transistor.
 6. The article of claim 5, further comprisinga timing capacitor connected to the base of the n-type transistor andconfigured to be charged when the two transistors are off and dischargedwhen the two transistors are on, wherein: the charging of the timingcapacitor causes the two transistors to turn on; and the discharging ofthe timing capacitor contributes to a current pulse through the twotransistors.
 7. The article of claim 1, wherein: the first transistor isthe p-type transistor; the second transistor is the n-type transistor;and the positive-feedback capacitor is connected between the collectorof the p-type transistor and the base of the n-type transistor.
 8. Thearticle of claim 7, further comprising a timing capacitor connected tothe base of the p-type transistor and configured to be charged when thetwo transistors are off and discharged when the two transistors are on,wherein: the charging of the timing capacitor causes the two transistorsto turn on; and the discharging of the timing capacitor contributes to acurrent pulse through the two transistors.
 9. The article of claim 1,wherein the secondary-side magnetically coupled conductor is connectedin series between the emitter of the n-type transistor and the emitterof the p-type transistor.
 10. The article of claim 9, wherein a catchdiode is connected in parallel with the secondary-side magneticallycoupled conductor between the emitter of the n-type transistor and theemitter of the p-type transistor.
 11. The article of claim 9, wherein: asecondary-side switch is connected in series with a catch diode; thesecondary-side switch and the catch diode are connected in parallel withthe secondary-side magnetically coupled conductor between the emitter ofthe n-type transistor and the emitter of the p-type transistor; theprimary side further comprises a data state detector connected to theprimary-side magnetically coupled conductor; the secondary-side switchis controllable to transmit data from the secondary side via thesecondary- and primary-side magnetically coupled conductors to theprimary side; and the data state detector detects the transmitted data.12. The article of claim 1, further comprising an output load connectedto the output port.
 13. The article of claim 1, wherein the secondaryside further comprises synchronous rectification circuitry 148 thatperforms synchronous rectification for the flyback converter based on acontrol voltage received from the demand pulse generator.
 14. Thearticle of claim 13, wherein the control voltage is at the collector ofthe n-type transistor.